Qingshuang Liang

Compositionally tunable Cu2Sn(SxSe1−x)3 nanocrystals: facile direct solution-phase synthesis, characterization, and scalable procedure

In this paper, we report a facile, low-cost synthesis of Cu2Sn(SxSe1−x)3 colloidal nanocrystals (NCs) by heating a mixture of metal salts, sulfur powder, selenium powder, oleylamine and dodecanethiol. The composition of the Cu2Sn(SxSe1−x)3 NCs could be tuned across the x range from 0 to 1 by modulating the molar ratio of the S/Se precursors. The lattice parameters (a and c) of the Cu2Sn(SxSe1−x)3 NCs, calculated from X-ray diffraction patterns, were consistent with Vegards law, confirming the formation of homogeneous nanocrystals. The X-ray diffraction and transmission electron microscopy results indicated that the as-prepared Cu2Sn(SxSe1−x)3 NCs had a monoclinic structure. The UV-visible absorption spectra of the Cu2Sn(SxSe1−x)3 NCs revealed that the band gap of the nanocrystals could be tailored from 1.55 to 1.87 eV by decreasing the Se content. Additionally, compared with the more commonly used hot injection method, the procedure developed here is highly suitable for large-scale colloidal nanocrystal production, which we tested by performing a gram-scale synthesis.

B-site ordering induced suppression of magnetic cluster glass and dielectric anomaly in La2−xBixCoMnO6

We report the heat, magnetic, and dielectric properties of La2−xBixCoMnO6 with a series of Bi doping concentrations, focusing especially on the impact of A-site doping on B-site ordering. We demonstrate that the B-site ordering is enhanced via the Bi doping, resulting in a suppressed cluster-glass behavior, larger dielectric constant, and smaller tangent loss. Surprisingly, a pronounced step-like dielectric anomaly turns up near the spin-freezing temperature in the Bi-free oxide, which is suppressed significantly after Bi doping. We attribute the suppression of anomaly to the lessened amount of antisite defects at the B sites and the associated strengthened electronic localization.

Synergistic effects of intrinsic cation disorder and electron-deficient substitution on ion and electron conductivity in La1-xSrxCo0.5Mn0.5O3-δ (x = 0, 0.5, and 0.75).

The effects of intrinsic cation disorder and electron-deficient substitution for La1-xSrxCo0.5Mn0.5O3-δ (LSCM, x = 0, 0.5, and 0.75) on oxygen vacancy formation, and their influence on the electrochemical properties, were revealed through a combination of computer simulation and experimental study. First-principles calculations were first performed and found that the tendency of the oxygen vacancy formation energy was Mn(3+)-O*-Mn(4+) < Co(2+)-O*-Co(3+) < Co(2+)-O*-Mn(4+), meaning that antisite defects not only facilitate the formation of oxygen vacancy but introduce the mixed-valent transition-metal pairs for high electrical conductivity. Detailed partial density of states (PDOS) analysis for Mn on Co sites (MnCo) and Co on Mn sites (CoMn) indicate that Co(2+) is prone to being Co(3+) while Mn(4+) is prone to being Mn(3+) when they are on antisites, respectively. Also it was found that the holes introduced by Sr tend to enter the Co sublattice for x = 0.5 and then the O sublattice when x = 0.75, which further promotes oxygen vacancy formation, and these results are confirmed by both the calculated PDOS results and charge-density difference. On the basis of microscopic predictions, we intentionally synthesized a series of pure LSCM compounds and carried out comprehensive characterization. The crystal structures and their stability were characterized via powder X-ray Rietveld refinements and in situ high-temperature X-ray diffraction. X-ray photoelectron spectroscopy testified to the mixed oxidation states of Co(2+)/Co(3+) and Mn(3+)/Mn(4+). The thermal expansion coefficients were found to match the Ce0.8Sm0.2O2-δ electrolyte well. The electrical conductivities were about 41.4, 140.5, and 204.2 S cm(-1) at doping levels of x = 0, 0.5, and 0.75, and the corresponding impedances were 0.041, 0.027, and 0.022 Ω cm(2) at 850 °C, respectively. All of the measured results testify that Sr-doped LaCo0.5Mn0.5O3 compounds are promising cathode materials for intermediate-temperature solid oxide fuel cells.

Lanthanide contraction effect on crystal structures, magnetic, and dielectric properties in ordered double perovskites LnPbCoSbO6 (Ln = La, Pr, Nd)

The crystal structures, magnetic, and dielectric properties for the ordered double perovskites LnPbCoSbO6 (Ln = La, Pr, Nd) have been investigated. The crystal structure has been solved by Rietveld refinements of X-ray diffraction data in the monoclinic space group P21/n (No. 14). The Co2+ and Sb5+ ions are almost fully ordered over the B-site, and the octahedral framework displays significant tilting distortion according to the Glazers tilt system a–a–c+. As the result of lanthanide contraction from La3+ to Nd3+, the B-site sublattice distortions become stronger accompanying with the reduction of the tolerance factor and coordination number. The magnetization measurements show an antiferromagnetic ordering with large effective magnetic moments (μeff) suggesting that the orbital component is significant. The maximum values of isothermal magnetization increase with the decrease in radii of rare earth ions, which is attributed to the weakening of antiferromagnetic interaction via Co2+–O–Sb5+–O–Co2+ paths. ...